The invention relates to improvements in apparatus for manipulating sheets, especially groups of sheets which constitute portions of books, brochures or the like. More particularly, the invention relates to improvements in apparatus for singularizing successive stacks of superimposed groups of sheets in a bookbinding or other plant.
Swiss Pat. No. 645 294 discloses a machine which serves to simultaneously trim two or more edge faces of a stack of sheets, e.g., one or more signatures, brochures or the like. The output of such trimming machine (e.g., the number of cycles per unit of time) is a relatively small fraction of the output of a perfect binder which is often located ahead of the trimming machine. Therefore, it is customary to accumulate the groups of sheets issuing from a perfect binder into stacks of superimposed groups and to simultaneously trim successive stacks to thus compensate for the difference between the output of the perfect binder and the output of the trimming machine. The height of each stack is selected with a view to ensure that the trimming machine will be capable of properly trimming two or three sides of the entire stack of superimposed groups of sheets. Another factor which determines the height of successive stacks is the difference between the output of the machine which turns out the groups (such as the aforementioned perfect binder) and the output of the trimming machine.
Once the trimming operation is completed, the stacks of superimposed groups of sheets must be broken up (i.e., singularized) for further processing, e.g., for gathering into packages containing selected numbers of trimmed groups preparatory to storage, shipment to customers or distributors or to another destination. For example, magazines, advertising brochures and like groups of sheets must be provided with names and addresses of recipients and the properly addressed groups are thereupon assembled into packages for shipment or mailing to selected post offices or directly to subscribers.